Thanks for the replies so far everyone. The Ethernet connector is shielded, but my assumption is that the Cat5 cable used is usually NOT shielded.
The digital ground involved is not connected to chassis, which is plastic in this case. Jim Eichner, P.Eng. Manager - Compliance Engineering Xantrex Technology Inc. e-mail: jim.eich...@xantrex.com web: www.xantrex.com Confidentiality Notice: This email message, including any attachments, is for the sole use of the intended recipient(s) and may contain confidential and privileged information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply e-mail and destroy all copies of the original message. From: emc-p...@ieee.org Sent: Wednesday, March 07, 2007 2:30 PM To: emc-p...@ieee.org Subject: Re: Ethernet connector shield decoupling capacitor Chas, The original post states the Ethernet is shielded. That was indeed the basis of my response. Ken > From: "Grasso, Charles" <charles.gra...@echostar.com> > Date: Wed, 7 Mar 2007 14:26:42 -0700 > To: "Ken Javor" <ken.ja...@emccompliance.com>, <emc-p...@ieee.org> > Subject: RE: Ethernet connector shield decoupling capacitor > > Hi Ken. Is the assumption that the externally run Ethernet is > shielded? Then I can see how ground potentials can be as issue. > > Typically all the internal stuff is unshielded. > > Best Regards > Charles Grasso > Compliance Engineer > Echostar Communications Corp. > Tel: 303-706-5467 > Fax: 303-799-6222 > Cell: 303-204-2974 > Pager/Short Message: 3032042...@vtext.com > Email: charles.gra...@echostar.com > > -----Original Message----- > From: emc-p...@ieee.org > Sent: Wednesday, March 07, 2007 2:19 PM > To: emc-p...@ieee.org > Subject: Re: Ethernet connector shield decoupling capacitor > > I think there are others on this forum who understand this better than > I do; in fact I learned this from someone else on this forum. > Ethernet can run a long way, and if it connects two pieces of > equipment whose enclosures are at slightly different mains frequency > potentials, due to their green wires going to different grounds, that > can cause current to flow through an Ethernet shield grounded at both > ends. Hence the capacitive decoupling which is a high impedance at > the mains frequency. This answer assumes that your digital ground is > tied to chassis ground, which I believe is typical. > >> From: "Jim Eichner" <jim.eich...@xantrex.com> >> Date: Wed, 7 Mar 2007 12:05:08 -0800 >> To: <emc-p...@ieee.org> >> Subject: Ethernet connector shield decoupling capacitor >> >> We're being hit with a requirement that I don't understand. >> >> We are using a shielded Ethernet connector that contains the typical > 2kV >> cap from the common point of the 75 ohm resistors to the shield. >> This is used on the output of an off-the-shelf Ethernet transceiver >> module, and the mfr of that module is telling us we need to connect >> the connector shield to their digital ground through a 1nF 250V >> Y-cap, not directly. >> >> 1. Why not directly connect the shield to digital ground? >> >> 2. Why would a Y-cap be required? The cap would be joining two parts > of >> the same circuit, so it would not be across an isolation boundary. I >> can't think of a reason to require either the 250V rating or the Y >> rating. >> >> Any thoughts anyone? >> >> Thanks, >> >> Jim Eichner, P.Eng. >> Manager - Compliance Engineering >> Xantrex Technology Inc. >> e-mail: jim.eich...@xantrex.com >> web: www.xantrex.com >> >> Confidentiality Notice: This email message, including any >> attachments, is for the sole use of the intended recipient(s) and may >> contain confidential and privileged information. Any unauthorized >> review, use, disclosure or distribution is prohibited. If you are not >> the intended recipient, please contact the sender by reply e-mail and >> destroy all copies of the original message. >> - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________
